There are various narrow-directivity optical devices such as light-emitting diode (LED) optical products including lighting devices, projectors, flashlights, and headlights and taillights for use in automobiles and such a device usually includes a lens used to collect or collimate light emitted from a light source. Usually, a convex-shaped refraction lens is used as such a light-collecting or collimating lens. FIG. 14 shows a conventional TIR (Total Internal Reflection) lens member 1 which has been developed as a lens superior in light-collecting properties. The lens member 1 has a central axis AX and has a hollow portion centered at the central axis AX and an outer circumferential surface 1a positioned outward of the hollow portion in radial directions perpendicular to the central axis AX. A light source 2 with its light-emitting surface facing the lens member 1 is disposed and the center of the light-emitting surface is aligned to coincide with the central axis AX of the lens member 1 that receives light emitted from the light source 2. Of the light, light rays emitted with tilts tilting closer to the radial directions relative to the central axis AX and received through an inner circumferential surface 1b that is a circumferential surface of the hollow portion of the lens member 1 are totally reflected at the outer circumferential surface 1a and exited from a light exit surface 1c of the lens member 1 toward the direction of extension of the central axis AX. It should be noted that the central axis AX is an imaginary line passing through the center of the lens member 1.
Japanese Patent Application Publication Nos. 1982-55002, 1984-119340 and 1993-281402 propose TIR lenses made in the form of a Fresnel lens in order to achieve reductions in height and thickness.
Since light emitted from a light source with a large light-emitting surface is more spreading than light from a light source with a small light-emitting surface, the conventional TIR lens shown in FIG. 14, for example, has the following problem. Accordingly, even if a light source is arranged with its emitted light passing through such a TIR lens, light-collecting efficiency with the TIR lens is decreased when a light source with a large light-emitting surface is used. In particular, when a light source including a plurality of LED elements arranged in plane is used as the light source 2, since the plurality of LED elements individually emit light and all together constitute a light-emitting surface of the light source 2, the light-emitting surface inevitably become large and it becomes difficult to achieve an efficient light-collecting or collimating effect with such a conventional lens.